Hello girls! Milk came on the second day, my breasts swelled up a lot…

Hello girls! Milk came on the second day, my breasts swelled up a lot. The baby eats well, but I can't feed him quickly enough, as my breast fills up pretty fast, becoming hard. When strong surges come, I don't pump much because of the strong pain. Yesterday we weighed the baby on the third day, he lost 10 grams from his initial weight... when will these surges end and how can I ease the pain?